1. Field of the Invention
This invention relates generally to the directed self-assembly (DSA) of block copolymers (BCPs), and more particularly to the DSA of BCPs to make an etch mask for pattern transfer into a substrate.
2. Description of the Related Art
Directed self-assembly (DSA) of block copolymers (BCPs) has been proposed for making imprint templates. Imprint templates have application in making patterned-media magnetic recording disks and in semiconductor manufacturing, for example, for patterning parallel generally straight lines in MPU, DRAM and NAND flash devices. DSA of BCPs by use of a patterned sublayer for the BCP film is well-known. After the BCP components self-assemble on the patterned sublayer, one of the components is selectively removed, leaving the other component with the desired pattern, which can be used as an etch mask to transfer the pattern into an underlying substrate. The etched substrate can be used as an imprint template.
With the prior art method of DSA of BCP thin films, the quality of the self-assembled pattern depends upon a number of factors, including film thickness, the acceptable defect density, the density multiplication factor, the chemistry of the patterned sublayer and individual stripe width of the patterned sublayer. The design of a process to have a large process window for one parameter usually implies that the process window for the other parameters gets reduced or compromised. For example, thicker BCP films are desirable for pattern transfer into the template; however, a thicker film results in higher defect densities or in a lower tolerance for a high density multiplication factor. Conversely, if a higher density multiplication factor is desired, or if more tolerance is needed for the width of the stripes, the film thickness needs to be reduced considerably to avoid a large defect density.
What is needed is an improved method for DSA of BCPs that allows for a large process window.